A typical disk drive has most of the electronics and firmware contained in a system-on-a-chip (SOC), which includes the read/write channel as well as the servo system. Additional electronics that provide an interface between the read/write channel and the plurality of read and write transducers (heads) are contained in preamplifier read/write (RW) ICs. A separate preamplifier (preamp) is used for each slider which contains a pair of read and write heads. The functioning of the preamps is controlled by setting parameter values in registers in the preamp by sending serial data to the preamp. Parameters can include write current value (Iw), overshoot amplitude value, overshoot duration value and thermal fly-height control (TFC).
Thermal fly-height control is a problem which has generated a variety of designs. For example, U.S. Pat. No. 7,457,072 to Dieron, et al. (Nov. 25, 2008) describes fly-height compensation for disk surface variations as a function of both the track, and the sector or sectors within the track, where data is to be read or written. The fly-height actuator can be a thermal actuator that includes heater located on the slider near the read/write head. The fly-height controller (FHC) for the thermal actuator stores band control signal values representative of heater power to be applied to the thermal actuator when reading or writing to a data track in the associated band of tracks. The FHC also either calculates from a programmed equation or recalls sector control signal (SCS) values representative of an heater power increment to be applied to the thermal actuator depending on the sector or sectors where data is to be written. The FHC sums the appropriate SCS value with the appropriate BCS value to achieve the desired heater power, resulting in the optimal fly-height not only for the selected band but also for the selected sector or sectors.
U.S. Pat. No. 7,023,647 to Bloodworth, et al. (Apr. 4, 2006) the fly height controller includes circuitry for adjusting the current through heat element resistor during transitions between read and write disk operations. These adjustments are applied in the form of relatively brief overdrive (high current to heat element resistor) and underdrive (low current to heat element resistor) pulses, each of which assist in the settling of the steady-state temperature of heads. The duration of the overdrive and underdrive pulses may be programmed by way of a timer, or alternatively may be manually controlled via a serial interface to fly height controller.
One approach to rotational TFC uses with an analog input to the preamp using an external digital-analog-converter (DAC). One disadvantage of this system is that only one parameter can be adjusted. In addition the external DAC requires an analog line to the preamp and noise on the analog line causes error in fly-height.
One aspect of the problem being addressed by the invention is the relatively slow nature of the process of setting parameters using serial communication methods. For example, in the prior art to update the DAC code number the entire DAC code number including a plurality of bits has to be sent to the preamp chip. Sending the required bits serially might require >300 ns, for example, per register write, and this process is too slow for the short available windows when there is no reading or writing underway in the gap area and, therefore, no risk of interference signals. The short read-to-write and write-to-read time gaps occur in each sector between the servo area and data area. Sending serial data to the preamp when a read signal or write signal is being processed can result in interference between the wires going to/from preamp.
For improved performance, there is a need to be able to update some or all of the preamplifier parameters within a single rotation of the disk. However, the conventional serial communication protocol to the preamplifiers is too slow to be completed in read/write gap windows and can interfere with read and write data causing jitter issues if serial data is transmitted outside of the gaps.